docs: def Pn(x):
      """Calculate Legendre polyomials P0 to P28 and returns them
      in a dictionary ``Pn``.
  
      :param float x:     argument to calculate Legendre polynomials
      :return Pn:         dictionary which contains order of Legendre polynomials
                          (from 0 to 28) as keys and the corresponding evaluation
                          of Legendre polynomials as values.
      :rtype:             dict
  
      """
      Pn = {}
      Pn['0'] = P0(x)
      Pn['1'] = P1(x)
      Pn['2'] = P2(x)
      Pn['3'] = P3(x)
      Pn['4'] = P4(x)
      Pn['5'] = P5(x)
      Pn['6'] = P6(x)
      Pn['8'] = P8(x)
      Pn['10'] = P10(x)
      Pn['12'] = P12(x)
      Pn['14'] = P14(x)
      Pn['16'] = P16(x)
      Pn['18'] = P18(x)
      Pn['20'] = P20(x)
      Pn['22'] = P22(x)
      Pn['24'] = P24(x)
      Pn['26'] = P26(x)
      Pn['28'] = P28(x)
      return Pn